Thanks Steve and Lothar
@Lothar I think I see what you are getting at, cool technique, but it still isn't giving the desired ease in/out effect.
@Steve Pedler I'm actually fine with having the smaller particles scale up faster, what I care about is the easing curve. It's a shame if it can't be done. It would be really nice when using bigger particles, like when using the xpGenerator to attach geometry. Consider it a feature request, I have needed it often, but until now I have lived with the linear easing.